Apparatus for treating solids in fluids



June 13, 1944. BAR 2,351,091

APPARATUS FOR TREATING SOLIDS IN FLUIDS Filed Dec. 19, 1941 FIGJ.

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Patented June 13, 1944 APPARATUS FOR. TREATING SOLIDS IN FLUIDS PeterJoachim Bar, Twickenliam, England Application December 19, 1941, SerialNo. 423,674 In Great Britain December 24, 1940 6 Claims.

This invention relates to improvements in floating contact treatment ofsolid particles in gas or vapour for the purpose of drying, calcining,heating, cooling, mixing, crystallising, carbonising, or for performingchemical reactions between solids and a gas, such as gas producing,combustion or others.

The object of the invention is to provide for control of the duration ofthe floating contact treatment and for improved control of conditions ofsuch treatment. This object is achieved by floating contact treatment ina closed circuit in such manner that the conditioning fluid will berapidly renewed whereas the solid particles will, in the average, besubjected to prolonged treatment.

According to this invention, both, solid particles and gas, are keptmoving in a closed circuit for a controllable period of time. As aconsequence of this, conditions of treatment can be freely selected inaccordance with the properties of the material treated and the treatmentdesired, because the duration of treatment can be adapted to thesefreely selected conditions of treatment.

Preferably, solid particles and gas are circulated together. Fresh gasis continuously introduced into the circuit, and an equivalent amount ofgas is continuously withdrawn from the circuit. It is an essentialfeature of the invention that solid particles are continuously ordiscontinuously introduced into the circuit in such manner that theybecome suspended in the gas and are carried along by the gas. Thisinvolves obvious limits as regards maximum size of solid particlesandminimum velocity required for keeping the solid particles insuspension.

It is a further essential feature of this invention that the finishedproduct-that is those solid particles, the treatment of which iscompleted are withdrawn from the circuit suspended in the gas that iswithdrawn. This means, it is an essential feature of this invention thatisolated solid particles are not taken out of the circuit, and

no separator for isolating finished solids from the "gas is inserted inthe circuit. Only after having been withdrawn from the circuit, theexhaust gas withdrawn per unit time, is higher than the quantity of gascirculated as compared with the quantity of gas introduced andwithdrawn.

In order to be morev clearly understood, the invention may now bedescribed more in detail with reference to the accompanying drawing,which illustrates, .in a diagrammatic manner, three examples of the manyalternative ways in which the invention may be carried into eifect.

Referring first to Figure 1, the solid particles to be treated are fedat point I into the ring duct 2 in such manner that these solid particleare carried along by the gas or vapour flowing in this duct.

Fresh gas is introduced into the ring duct at point 3, and an equivalentamount of gas is withdrawn at point 4 and passed into separator 5.

Movement in the ring duct at a velocity sufficient to keep the solidparticles floating is maintained by means of the injector principle. Thefresh gas is introduced at point 3 in a strong jet at such highvelocity, that gas and solids are entrained from point 4 to point 3,mixed with the incoming jet, and the mixture then circulated around thering duct again to point 4.

The point of withdrawal is designed as a classifier with the object ofreleasing only a small quantity of finished solids with th gas that iswithdrawn and passed into separator 5, whereas the greater part of thesolid particles is passed from point 4 to point 3 and thus retained inthe circuit. As shown diagrammatically in the rawing, the withdrawalpipe I2 is arranged at the inner side of a bend of the ring duct 2.Owing to centrifugal force, the solid particles are bound to pass alongthe outer part of a bend, so that only a comparatively limited amount ofthe finest and lightest solid particles is carried along into separator5, whereas the bulk of the solids is retained in the circuit.

Thus, the classifier has both, a quantitative and a qualitativeselecting effect. A quantitative selecting effect because, in theaverage, each particle will make a number of circulations before beingcarried away from the circuit at point 4,

will be entrained with the exhaust gas, whereas coarse and heavyparticles will be retained in the circuit, and it can, in most cases, beassumed- ,though with certain exceptions-that the finished product islighter and finer than those particles, which have not yet undergonetreatment for a sumcient length of time. The feed of "solidparticlesinto the ring duct 2 is so arranged that the particles are fedfrom shopper 6 through a feeder or air lock I at a controllable rate,continuously or discontinuously. By controlling the rate of feed and thevelocity in ring duct 2, the period, during which the solid particlesremain in the circuit, can be controlled within wide limits, because theselecting efiiciency of a classifier depends largely upon the rate, atwhich solids are passed into it.

The fresh gas jet, which enters the ring duct at point 2, is blown in byfan 8 through conduit I. In order to show diagrammatically thedifference between fresh gas and exhaust gas, it is assumed that thefresh gas is hot. This will be true for most of the purposes, for whichthe invention may be used. Therefore, all drawings show a furnace orheater I as a symbol for the source, from which the fresh gas comes.Actually. conditions in the circuit depend, or course, upon the kind oftreatment required in each individual case. In the case of drying,calcining and heating, the fresh gas is warm or hot-for the purpose ofcooling, the fresh gas must be cold-for the purpose of chemicalreactions, the fresh gas must have certain chemical properties.

The exhaust gas. after passing separator 5, is blown out through conduitll, whereas the finished product is discharged through conduit l4 andair lock it. The separator, in which the finished product is isolatedfrom the exhaust gas, can he of am! known kind such as a settlingchamber, bag filter, electrostatic precipitator, cy-

clone or other kind. In all the accompanying drawings, a diagrammaticview of a cyclone is shown as a symbol for a separator.

The feed of solids can be at any point of the circular duct 2 orthefresh gas duct 9. Figure 2 shows feed into fresh gas duct, so thatfresh gas and fresh solids enter the ring duct together. whereas twoother drawings show feed into the ring duct 2 itself.

All the drawings show the fan outside the ring duct itself, and aninjector for maintaining circulation in the ring duct. The fan may blowthe fresh gas jet in, as shown in Figures 1 and 3, or the fan may drawgas out of the ring as shown in Figure 2.

The classifier arranged at that point of the ring duct, at which theexhaust gas is withdrawn, can also be designed in many alternative ways.A'preferable design is shown in Figure 3, whereas, in the Otherdrawings, the classifier is symbolised by showing the exhaust ductbranched off at the inner side of a curved portion of the ring duct.

Referring now to Figure 2, the ring duct 2 with injector 3 andclassifier 4 are the same as in Figure 1. The solids are fed from hopper8 through feeder 1 into duct 2 and enter the ring duct 2 together withfresh gas.

Fan to is so arranged that the fan draws the gas through the ring duct.Accordingly, in the arrangement as shown in Figure 2, the ring duct iskept under a slight vacuum, whereas in the arrangement as shown inFigure 1, the ring duct is kept under a slight pressure. In either case,the kinetic energy required at point 3 for the fresh .gas jet determinesthe amount of vacuum or pressure required.

furnace in through conduit I1.

As distinct from Figure 1, a double circuit shown in Figure 2. This isof advantage when treatment in ring duct 2 has to be carried out withina close range of conditions, for instance temperature conditions. It maythen increase the thermal efliciency of the system to dilute the freshgas coming from furnace ID with some exhaust gas, and to introduce thismixture into ring duct 2. Accordingly, Figure 2 shows how part of thegas withdrawn from ring duct 2 through conduit l2, fan to and conduit I8is recirculated through conduit l8 and mixed with fresh gas coming fromAn adjustable valve I9 is provided in conduit l8, to determine theproportion of gas recirculated in such way.

Referring now to Figure 3, this shows an arrangement, which is the sameas that in Figure 1. except that a two stage centrifugal classifier isprovided, by which the proportion of solid matter, which is carried awayto the separator, is still better controlled.

In place of conduit l2 of Figure 1 branched oil from the inner side of abend of duct 2, a drum 20 is provided communicating with the ring ductthrough an opening 2|, also at the inner side of a bend of the ringduct, in such way that gas passing into said drum through opening 2|will rotate in the drum in the same direction of rotation as in thecurved portion of the ring duct, which it has just left. Leading axiallyfrom the centre of this drum, is a conduit 22, which leads to thesepfirat0r 5. Most of the solid particles are, in

the first instance, retained in ring duct 2 by centrifugal force, only asmall portioh passing with the gas through opening 2| into drum 20.Here, a further stage of classification is now effected. Within thedrum, the greater part of the solid particles are again kept near theperiphery by centrifugal force, and these return into ring duct 2through opening 2|, only a small portion finally passing out intoconduit 22. Preferably, the drum is not completely circular but voluteshaped.

In order that the selecting effect of the classifier may becontrollable, a deflector 23 hinged at 24 is provided in opening 2 I.This deflector may either be inclined towards the conduit 2 or towardsthe drum 20, for respectively rendering more diflicult or more easy theentrainment of solid particles into the drum. A similar flap 25 is alsoprovided hinged at 26 at the point where conduit 9 joins the ring duct2. By adjusting this flap, the injector effect may be controlled.

In all other respects, this figure is the same as Figure 1, and likereferences are employed to designate the same parts.

It may be emphasised that the shape of the ring duct is, obviously,altogether immaterial for the principal features of this invention. Anykind and shape of duct may be used, the cross section of the duct may beconstant or vary in various parts of the duct, the duct may extend invertical or horizontal direction, the duct may be in one plane or not,and round, rectangular or irregularly shaped piping may b used. The oneessential feature is that the duct is endless. so that completecirculation of some fluid and some solid particles is possible.

In order to illustrate the invention further, the following practicalexample is added:

It may be assumed, by way of example, that Figure 1 shows a pneumaticring dryer used for the purpose of drying 1,250 ib./hr. of grass from 82to 10% moisture content. Accordingly, 1,250 lb./hr. of grass with 82%moisture are introduced continuously from hopper 6, and the plant has tobe so designed and operated, that 250 lb./hr. of

dried grass containing 10% residual moisture are continuously dischargedfrom separator 8. This necessitates the evaporation of 1,000 lb./hr. ofwater, corresponding to a net heat consumption of about 1,000,000 B. T.U./hr. The total net heat consumption of the dryer including heating upof material and losses of sensible heat can be estimated to be about1,250,000 B. T. U./hr.

As suitable working temperatures, 380 F. at the injector, point 3, and200 F. exhaust temperature at and after point I may be selected. Heatthroughput and temperature range as specified lead to a' quantity of26.500 lb./hr. of gas to be circulated in ring duct 2.

Fan and injector may then be so designed and controlled, that half thecirculating quantity of gas, i. e. 13,250 lb./hr is withdrawn throughconduit l2, whereas the other 13,2'50 lb./hr. of gas carrying the mainstream of uncompletely dried grass are passed from point 4 to theinjector at point 3. Here, another 13,250 lb/hr. of fresh gas areintroduced serving to make up for the exhaust gas and as driving jet tomaintain circulation. In order to raise the temperature of the mixtureafter point 3 to 380 F., whereas the gas coming from point 4 has 200 F.,the temperature of the fresh gas coming from duct 9 will have to be 560F.

Ring duct 2 has to be so designed as to allow for passage of 26,500lb./hr. of gas, and the duct must have suflicient length to allow forthespecifled temperature drop of the gas from 380 F. to 200 F. to beachieved by exchange of heat with the moist surface of the grasssuspended in the gas. The length of the duct and the velocities may beassumed to be such that one full circulation oi grass from the injectorto the classifier takes 2 seconds. n the other hand, it may be assumedthat the drying time required for reducing the moisture content of thegrass from 82% to 10% when in violent floating contact with gas underprevailing velocity and temperature conditions as described, is of theorder of one minute. This means that, in the average, each grass bladehas to make 30 full circulations before being finished. Since input andoutput amount to 225 lb./hr. of bone dry grass, the rate of circulationof bone dry grass in the ring duct will have to be 6.750 lb./h r.classifier has to be so designed and controlled, that out of the heavystream of uncompletely dried grasscirculating in the ring duct, only 250ib./hr. of grass of l0%moisture are entrained with the exhaust gas intoseparator 5.

I claim:

1. In an apparatus for treating solid particles in a conditioning fluidcomprising an endless duct, an injection nozzle for introducing fluidinto said endless duct and maintaining continuous circulation of fluidwithin said duct, a deflector plate forming one wall of said nozzle andserving for controlling the fluid jet produced by the nozzle, means forintroducing solid particles into said endless duct, said duct having anoutlet located approximately opposite said inj ction nozzle, and a tanoutside the endless duct producing the necessary pressure drop foroperating the nozzle and for passing fluid through said outlet.

2. In an apparatus for treating solid particles in a conditioning fluidcomprising an endless Accordingly. the

duct, an injection nozzle for introducing fluid into said endless ductand maintaining continuous circulation of fluid within said duct, adeflector plate forming one wall of said nozzle and serving forcontrolling the fluid jet produced by the nozzle, means for introducingsolid particles into said endless duct, said duct having an outletlocated approximately opposite said inJection nozzle, a deflector insaid outlet of the endless duct, and a fan outside the endless duct forproducing the necessary pressure drop for operating the nozzle and forpassing fluid through said outlet. 3. In an apparatus for treating solidparticles in a conditioning fluid comprising an endless duct, aninjection nozzle for introducing fluid into said endless duct and formaintaining continuous circulation of fluid within said duct, means forintroducing solid particles into said endless duct, said duct having anoutlet located approximately opposite said injection nozzle, and a drumhaving a tangential inlet and axial outlet so connected to said endlessduct that they have a common wall, said wall having an opening thereinforming the outlet of the endless duct and, at the same time, the inletof the drum.

4. An apparatus for treating solid particles in a fluid comprising anendless duct, means for continuously circulating fluid within saidendless duct as well as for introducing fluid into said duct, means forwithdrawing fluid from said duct, a feeding device for introducing solidparticles into said duct, a drum with a tangential inlet and axialoutlet connected to said endless duct in such a way that they have acommon wall, an opening in said common wall being the outlet of theendless duct and, at the same time, the inlet of the drum, and a hingeddeflector in said opening, said deflector forming part of said commonwall.

5. An apparatus for treating solid particles in a conditioning fluidcomprising an endless duct, an inlet conduit disposed at an acute angleto said endless duct, an outlet on the inner side of a bend of saidendless duct. a fan passing fluid through the whole apparatus andproducing such a pressure drop between said inlet conduit and saidendless duct that fluid is injected into the endless duct andcirculation or fluid maintained throughout the endless duct, a hingedflap at the point where the inlet conduit joins the endless duct, meansfor heating the fluid prior to being injected into said endless duct,means for introducing solid particles into said endless duct, aclassifier connected to the outlet of said endless duct and a hingeddeflector arranged at this outlet to control the release of solidparticles from the endless duct.

6. An apparatus for treating solid particles in a fluid comprising anendless duct, means for introducing solid particles into said endlessduct, means for continuously circulating a particle floating fluidwithin said endless duct as well as for introducing fluid into saidduct, and means for withdrawing fluid from said duct. said lastnamedmeans including a drum having a tangential inlet and axial outletconnected to said endles duct in such way that they have a common wall,and said wall having an opening therein forming the outlet or theendless duct and, at the same time, the inlet of the drum.

PETER JOACHIM BAR.

